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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 MILE N. Cam-Winget, Ed. 3 Internet-Draft S. Appala 4 Intended status: Standards Track S. Pope 5 Expires: December 28, 2018 Cisco Systems 6 P. Saint-Andre 7 Mozilla 8 June 26, 2018 10 Using XMPP for Security Information Exchange 11 draft-ietf-mile-xmpp-grid-06 13 Abstract 15 This document describes how to use the Extensible Messaging and 16 Presence Protocol (XMPP) to collect and distribute security-relevant 17 information between network-connected devices. To illustrate the 18 principles involved, this document describes such a usage for the 19 Incident Object Description Exchange Format (IODEF). 21 Status of This Memo 23 This Internet-Draft is submitted in full conformance with the 24 provisions of BCP 78 and BCP 79. 26 Internet-Drafts are working documents of the Internet Engineering 27 Task Force (IETF). Note that other groups may also distribute 28 working documents as Internet-Drafts. The list of current Internet- 29 Drafts is at https://datatracker.ietf.org/drafts/current/. 31 Internet-Drafts are draft documents valid for a maximum of six months 32 and may be updated, replaced, or obsoleted by other documents at any 33 time. It is inappropriate to use Internet-Drafts as reference 34 material or to cite them other than as "work in progress." 36 This Internet-Draft will expire on December 28, 2018. 38 Copyright Notice 40 Copyright (c) 2018 IETF Trust and the persons identified as the 41 document authors. All rights reserved. 43 This document is subject to BCP 78 and the IETF Trust's Legal 44 Provisions Relating to IETF Documents 45 (https://trustee.ietf.org/license-info) in effect on the date of 46 publication of this document. Please review these documents 47 carefully, as they describe your rights and restrictions with respect 48 to this document. Code Components extracted from this document must 49 include Simplified BSD License text as described in Section 4.e of 50 the Trust Legal Provisions and are provided without warranty as 51 described in the Simplified BSD License. 53 Table of Contents 55 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 56 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2 57 3. Architecture . . . . . . . . . . . . . . . . . . . . . . . . 4 58 4. Workflow . . . . . . . . . . . . . . . . . . . . . . . . . . 5 59 5. Service Discovery . . . . . . . . . . . . . . . . . . . . . . 7 60 6. Publish-Subscribe . . . . . . . . . . . . . . . . . . . . . . 8 61 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 62 8. Security Considerations . . . . . . . . . . . . . . . . . . . 11 63 8.1. Trust Model . . . . . . . . . . . . . . . . . . . . . . . 12 64 8.2. Threat Model . . . . . . . . . . . . . . . . . . . . . . 13 65 8.3. Countermeasures . . . . . . . . . . . . . . . . . . . . . 17 66 8.4. Summary . . . . . . . . . . . . . . . . . . . . . . . . . 20 67 9. Privacy Considerations . . . . . . . . . . . . . . . . . . . 21 68 10. Operations and Management Considerations . . . . . . . . . . 21 69 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 22 70 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 22 71 12.1. Normative References . . . . . . . . . . . . . . . . . . 22 72 12.2. Informative References . . . . . . . . . . . . . . . . . 23 73 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23 75 1. Introduction 77 This document describes "XMPP-Grid": a method for using the 78 Extensible Messaging and Presence Protocol (XMPP) [RFC6120] to 79 collect and distribute security-relevant information among network 80 platforms, endpoints, and any other network-connected device. Among 81 other things, XMPP provides a publish-subscribe service [XEP-0060] 82 that acts as a broker, enabling control-plane functions by which 83 entities can discover available information to be published or 84 consumed. Although such information can take the form of any 85 structured data (XML, JSON, etc.), this document illustrates the 86 principles of XMPP-Grid with examples that use the Incident Object 87 Description Exchange Format (IODEF) [RFC7970]. 89 2. Terminology 91 This document uses XMPP terminology defined in [RFC6120] and 92 [XEP-0060] as well as Security Automation and Continuous Monitoring 93 (SACM) terminology defined in [I-D.ietf-sacm-terminology]. Because 94 the intended audience for this document is those who implement and 95 deploy security reporting systems, in general the SACM terms are used 96 (however, mappings are provided for the benefit of XMPP developers 97 and operators). 99 Broker: In SACM, a specific type of controller containing control 100 plane functions; as used here, the term refers to an XMPP publish- 101 subscribe service. 103 Broker Flow: In SACM, a method by which security-related information 104 is published and consumed in a mediated fashion through a Broker. 105 In this flow, the Broker handles authorization of Consumers and 106 Providers to Topics, receives messages from Providers, and 107 delivers published messages to Consumers. 109 Consumer: In SACM, an entity that contains functions to receive 110 information from other components; as used here, the term refers 111 to an XMPP publish-subscribe Subscriber. 113 Controller: In SACM, a "component containing control plane functions 114 that manage and facilitate information sharing or execute on 115 security functions"; as used here, the term refers to an XMPP 116 server, which provides core message delivery [RFC6120] used by 117 publish-subscribe entities. 119 Node: The XMPP term for a Topic. 121 Platform: Any entity that connects to the XMPP-Grid in order to 122 publish or consume security-related data. 124 Provider: In SACM, an entity that contains functions to provide 125 information to other components; as used here, the term refers to 126 an XMPP publish-subscribe Publisher. 128 Publisher: The XMPP term for a Provider. 130 Publish-Subscribe Service: The XMPP term for the kind Broker 131 discussed here. 133 Subscriber: The XMPP term for a Consumer. 135 Topic: A contextual information channel created on a Broker at which 136 messages generated by a Provider are propagated in real time to 137 one or more Consumers. Each Topic is limited to a specific type 138 and format of security data (e.g., IODEF) and provides an XMPP 139 interface by which the data can be obtained. 141 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 142 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 143 document are to be interpreted as described in [RFC2119]. 145 3. Architecture 147 The following figure illustrates the architecture of XMPP-Grid. 149 +--------------------------------------+ 150 | +--------------------------------------+ 151 | | +--------------------------------------+ 152 | | | | 153 +-| | Platforms | 154 +-| | 155 +--------------------------------------+ 156 / \ / \ / \ 157 / C \ / \ / \ 158 - o - - d - - - 159 ||n||A | a |B | |C 160 ||t|| | t | | | 161 - r - - a - | | 162 \ o / \ / | | 163 \ l / \ / | | 164 /|---------------------|\ | | 165 /|----/ \--------| d |--|\ 166 / / Controller \ ctrl | a | \ 167 \ \ & Broker / plane | t | / 168 \|----\ /--------| a |--|/ 169 \|---------------------|/ | | 170 / \ / \ | | 171 / C \ / \ | | 172 - o - - d - | | 173 ||n||A | a |B | |C 174 ||t|| | t | | | 175 - r - - a - - - 176 \ o / \ / \ / 177 \ l / \ / \ / 178 +------------------------------------+ 179 | |-+ 180 | Platforms | | 181 | | |-+ 182 +------------------------------------+ | | 183 +------------------------------------+ | 184 +------------------------------------+ 186 Figure 1: XMPP-Grid Architecture 188 Platforms connect to the Controller (XMPP server) to authenticate and 189 then establish appropriate authorizations and relationships (e.g., 190 Provider or Consumer) at the Broker. The control plane messaging is 191 established through XMPP and shown as "A" (control plane interface) 192 in Figure 1. Authorized nodes can then share data either thru the 193 Broker (shown as "B" in Figure 1) or in some cases directly (shown as 194 "C" in Figure 1). This document focuses primarily on the Broker Flow 195 for information sharing ("direct flow" interactions can be used for 196 specialized purposes such as bulk data transfer, but methods for 197 doing so are outside the scope of this document). 199 4. Workflow 201 A typical XMPP-Grid workflow is as follows: 203 a. A Platform with a source of security data requests connection to 204 the XMPP-Grid via a Controller (XMPP server). 206 b. The Controller authenticates the Platform. 208 c. The Platform establishes authorized privileges (e.g. privilege to 209 publish and/or subscribe to security data Topics) with a Broker. 211 d. The Platform can publish security-related data to a Topic, 212 subscribe to a Topic, query a Topic, or any combination of these 213 operations. 215 e. A Provider unicasts its Topic updates to the Grid in real time 216 through a Broker. The Broker handles replication and 217 distribution of the Topic to Consumers. A Provider can publish 218 the same or different data to multiple Topics. 220 f. Any Platform on the Grid can subscribe to any Topics published to 221 the Grid (as permitted by authorization policy), and as Consumers 222 will then receive a continual, real-time stream of updates from 223 the Topics to which it is subscribed. 225 The general workflow is summarized in the figure below: 227 +--------------+ +------------+ +---------------+ 228 | IODEF Client | | Controller | | IODEF Service | 229 | (Consumer) | | & Broker | | (Provider) | 230 +--------------+ +------------+ +---------------+ 231 | | | 232 | Establish XMPP | | 233 | Client Session | | 234 | (RFC 6120) | | 235 |--------------------->| | 236 | | Establish XMPP | 237 | | Client Session | 238 | | (RFC 6120) | 239 | |<------------------------| 240 | | Request Topic Creation | 241 | | (XEP-0060) | 242 | |<------------------------| 243 | | Topic Creation Success | 244 | | (XEP-0060) | 245 | |------------------------>| 246 | Request Topic List | | 247 | (XEP-0030) | | 248 |--------------------->| | 249 | Return Topic List | | 250 | (XEP-0030) | | 251 |<---------------------| | 252 | | | 253 | Query Each Topic | | 254 | (XEP-0030) | | 255 |--------------------->| | 256 | Return Topic Data | | 257 | Including Topic Type | | 258 | (XEP-0030) | | 259 |<---------------------| | 260 | | | 261 | Subscribe to IODEF | | 262 | Topic (XEP-0060) | | 263 |--------------------->| | 264 | Subscription Success | | 265 | (XEP-0060) | | 266 |<---------------------| | 267 | | Publish IODEF Incident | 268 | | (XEP-0060) | 269 | Receive IODEF |<------------------------| 270 | Incident (XEP-0060) | | 271 |<---------------------| | 272 | | | 274 Figure 2: IODEF Example Workflow 276 XMPP-Grid implementations MUST adhere to the mandatory-to-implement 277 and mandatory-to-negotiate features as defined in [RFC6120]. 278 Similarly, implementations MUST implement [XEP-0060] to facilitate 279 the asynchronous sharing for information. The Service Discovery per 280 [XEP-0030] SHOULD be implemented to facilitate the means to 281 dynamically discover the available information (Topics) to be 282 published or consumes. 284 The following sections provide protocol examples for the service 285 discovery and publish-subscribe parts of the workflow. 287 5. Service Discovery 289 Using the XMPP service discovery extension [XEP-0030], a Controller 290 enables Platforms to discover what information can be consumed 291 through the Broker, and at which Topics. As an example, the 292 Controller at 'security-grid.example' might provide a Broker at 293 'broker.security-grid.example' hosting a number of Topics. A 294 Platform at 'xmpp-grid-client@mile-host.example' would query the 295 Broker about its available Topics by sending an XMPP "disco#items" 296 request to the Broker: 298 302 303 305 The Broker responds with the Topics it hosts: 307 311 312 315 318 319 321 In order to determine the exact nature of each Topic (i.e., in order 322 to find topics that publish incidents in the IODEF format), a 323 Platform would send an XMPP "disco#info" request to each Topic: 325 331 333 The Broker responds with the "disco#info" description, which SHOULD 334 include an XMPP Data Form [XEP-0004] including a 'pubsub#type' field 335 that specifies the supported namespace (in this example, the IODEF 336 namespace defined in [RFC7970]): 338 342 344 345 346 347 348 http://jabber.org/protocol/pubsub#meta-data 349 350 351 urn:ietf:params:xml:ns:iodef-2.0 352 353 354 355 357 6. Publish-Subscribe 359 Using the XMPP publish-subscribe extension [XEP-0030], a Consumer 360 subscribes to a Topic and a Provider publishes information to that 361 Topic, which the Broker then distributes to all subscribed Consumers. 363 First, a Provider would create a Topic as follows: 365 369 370 371 372 373 Note: The foregoing example is the minimal protocol needed to create 374 a Topic with the default node configuration on the XMPP publish- 375 subscribe service specified in the 'to' address of the creation 376 request stanza. Depending on security requirements, the Provider 377 might need to request a non-default configuration for the node; see 378 [XEP-0060] for detailed examples. 380 Unless an error occurs (see [XEP-0060] for various error flows), the 381 Broker responds with success: 383 388 Second, a Consumer would subscribe as follows: 390 394 395 397 398 400 Unless an error occurs (see [XEP-0060] for various error flows), the 401 Broker responds with success: 403 407 408 412 413 415 Third, a Provider would publish an incident as follows: 417 421 422 423 424 430 431 492382 432 2015-07-18T09:00:00-05:00 433 434 435 contact@csirt.example.com 436 437 438 439 440 441 442 443 445 (The payload in the foregoing example is from [RFC7970]; payloads for 446 additional use cases can be found in [RFC8274].) 448 The Broker would then deliver that incident report to all Consumers 449 who are subscribe to the Topic: 451 455 456 457 458 464 465 492382 466 2015-07-18T09:00:00-05:00 467 468 469 contact@csirt.example.com 470 471 472 473 474 475 476 477 479 7. IANA Considerations 481 This document has no actions for IANA. 483 8. Security Considerations 485 An XMPP-Grid Controller serves as an controlling broker for XMPP-Grid 486 Platforms such as Enforcement Points, Policy Servers, CMDBs, and 487 Sensors, using a publish-subscribe-search model of information 488 exchange and lookup. By increasing the ability of XMPP-Grid 489 Platforms to learn about and respond to security-relevant events and 490 data, XMPP-Grid can improve the timeliness and utility of the 491 security system. However, this integrated security system can also 492 be exploited by attackers if they can compromise it. Therefore, 493 strong security protections for XMPP-Grid are essential. 495 This section provides a security analysis of the XMPP-Grid data 496 transfer protocol and the architectural elements that employ it, 497 specifically with respect to their use of this protocol. Three 498 subsections define the trust model (which elements are trusted to do 499 what), the threat model (attacks that can be mounted on the system), 500 and the countermeasures (ways to address or mitigate the threats 501 previously identified). 503 8.1. Trust Model 505 The first step in analyzing the security of the XMPP-Grid transport 506 protocol is to describe the trust model, listing what each 507 architectural element is trusted to do. The items listed here are 508 assumptions, but provisions are made in the Threat Model and 509 Countermeasures sections for elements that fail to perform as they 510 were trusted to do. 512 8.1.1. Network 514 The network used to carry XMPP-Grid messages (i.e., the underlying 515 network transport layer over which XMPP runs) is trusted to: 517 o Perform best effort delivery of network traffic 519 The network used to carry XMPP-Grid messages is not expected 520 (trusted) to: 522 o Provide confidentiality or integrity protection for messages sent 523 over it 525 o Provide timely or reliable service 527 8.1.2. XMPP-Grid Platforms 529 Authorized XMPP-Grid Platforms are trusted to: 531 o Preserve the confidentiality of sensitive data retrieved via the 532 XMPP-Grid Controller 534 8.1.3. XMPP-Grid Controller 536 The XMPP-Grid Controller (including its associated Broker) is trusted 537 to: 539 o Broker requests for data and enforce authorization of access to 540 this data throughout its lifecycle 542 o Perform service requests in a timely and accurate manner 544 o Create and maintain accurate operational attributes 545 o Only reveal data to and accept service requests from authorized 546 parties 548 The XMPP-Grid Controller is not expected (trusted) to: 550 o Verify the truth (correctness) of data 552 8.1.4. Certification Authority 554 The Certification Authority (CA) that issues certificates for the 555 XMPP-Grid Controller and/or XMPP-Grid Platforms (or each CA, if there 556 are several) is trusted to: 558 o Ensure that only proper certificates are issued and that all 559 certificates are issued in accordance with the CA's policies 561 o Revoke certificates previously issued when necessary 563 o Regularly and securely distribute certificate revocation 564 information 566 o Promptly detect and report any violations of this trust so that 567 they can be handled 569 The CA is not expected (trusted) to: 571 o Issue certificates that go beyond the XMPP-Grid needs or other 572 constraints imposed by a relying party. 574 8.2. Threat Model 576 To secure the XMPP-Grid data transfer protocol and the architectural 577 elements that implement it, this section identifies the attacks that 578 can be mounted against the protocol and elements. 580 8.2.1. Network Attacks 582 A variety of attacks can be mounted using the network. For the 583 purposes of this subsection the phrase "network traffic" can be taken 584 to mean messages and/or parts of messages. Any of these attacks can 585 be mounted by network elements, by parties who control network 586 elements, and (in many cases) by parties who control network-attached 587 devices. 589 o Network traffic can be passively monitored to glean information 590 from any unencrypted traffic 592 o Even if all traffic is encrypted, valuable information can be 593 gained by traffic analysis (volume, timing, source and destination 594 addresses, etc.) 596 o Network traffic can be modified in transit 598 o Previously transmitted network traffic can be replayed 600 o New network traffic can be added 602 o Network traffic can be blocked, perhaps selectively 604 o A "Man In The Middle" (MITM) attack can be mounted where an 605 attacker interposes itself between two communicating parties and 606 poses as the other end to either party or impersonates the other 607 end to either or both parties 609 o Resist attacks (including denial of service and other attacks from 610 XMPP-Grid Platforms) 612 o Undesired network traffic can be sent in an effort to overload an 613 architectural component, thus mounting a denial of service attack 615 8.2.2. XMPP-Grid Platforms 617 An unauthorized XMPP-Grid Platform (one which is not recognized by 618 the XMPP-Grid Controller or is recognized but not authorized to 619 perform any actions) cannot mount any attacks other than those listed 620 in the Network Attacks section above. 622 An authorized XMPP-Grid Platform, on the other hand, can mount many 623 attacks. These attacks might occur because the XMPP-Grid Platform is 624 controlled by a malicious, careless, or incompetent party (whether 625 because its owner is malicious, careless, or incompetent or because 626 the XMPP-Grid Platform has been compromised and is now controlled by 627 a party other than its owner). They might also occur because the 628 XMPP-Grid Platform is running malicious software; because the XMPP- 629 Grid Platform is running buggy software (which can fail in a state 630 that floods the network with traffic); or because the XMPP-Grid 631 Platform has been configured improperly. From a security standpoint, 632 it generally makes no difference why an attack is initiated. The 633 same countermeasures can be employed in any case. 635 Here is a list of attacks that can be mounted by an authorized XMPP- 636 Grid Platform: 638 o Cause many false alarms or otherwise overload the XMPP-Grid 639 Controller or other elements in the network security system 640 (including human administrators) leading to a denial of service or 641 disabling parts of the network security system 643 o Omit important actions (such as posting incriminating data), 644 resulting in incorrect access 646 o Use confidential information obtained from the XMPP-Grid 647 Controller to enable further attacks (such as using endpoint 648 health check results to exploit vulnerable endpoints) 650 o Advertise data crafted to exploit vulnerabilities in the XMPP-Grid 651 Controller or in other XMPP-Grid Platforms, with a goal of 652 compromising those systems 654 o Issue a search request or set up a subscription that matches an 655 enormous result, leading to resource exhaustion on the XMPP-Grid 656 Controller, the publishing XMPP-Grid Platform, and/or the network 658 o Establish a communication channel using another XMPP-Grid 659 Platform's session-id 661 Dependencies of or vulnerabilities of authorized XMPP-Grid Platforms 662 can be exploited to effect these attacks. Another way to effect 663 these attacks is to gain the ability to impersonate an XMPP-Grid 664 Platform (through theft of the XMPP-Grid Platform's identity 665 credentials or through other means). Even a clock skew between the 666 XMPP-Grid Platform and XMPP-Grid Controller can cause problems if the 667 XMPP-Grid Platform assumes that old XMPP-Grid Platform data deserves 668 to be ignored. 670 8.2.3. XMPP-Grid Controllers 672 An unauthorized XMPP-Grid Controller (one which is not trusted by 673 XMPP-Grid Platforms) cannot mount any attacks other than those listed 674 in the Network Attacks section above. 676 An authorized XMPP-Grid Controller can mount many attacks. Similar 677 to the XMPP-Grid Platform case described above, these attacks might 678 occur because the XMPP-Grid Controller is controlled by a malicious, 679 careless, or incompetent party (either an XMPP-Grid Controller 680 administrator or an attacker who has seized control of the XMPP-Grid 681 Controller). They might also occur because the XMPP-Grid Controller 682 is running malicious software, because the XMPP-Grid Controller is 683 running buggy software (which can fail in a state that corrupts data 684 or floods the network with traffic), or because the XMPP-Grid 685 Controller has been configured improperly. 687 All of the attacks listed for XMPP-Grid Platform above can be mounted 688 by the XMPP-Grid Controller. Detection of these attacks will be more 689 difficult since the XMPP-Grid Controller can create false operational 690 attributes and/or logs that imply some other party created any bad 691 data. 693 Additional XMPP-Grid Controller attacks can include: 695 o Expose different data to different XMPP-Grid Platforms to mislead 696 investigators or cause inconsistent behavior 698 o Mount an even more effective denial of service attack than a 699 single XMPP-Grid Platform could 701 o Obtain and cache XMPP-Grid Platform credentials so they can be 702 used to impersonate XMPP-Grid Platforms even after a breach of the 703 XMPP-Grid Controller is repaired 705 o Obtain and cache XMPP-Grid Controller administrator credentials so 706 they can be used to regain control of the XMPP-Grid Controller 707 after the breach of the XMPP-Grid Controller is repaired 709 Dependencies of or vulnerabilities of the XMPP-Grid Controller can be 710 exploited to obtain control of the XMPP-Grid Controller and effect 711 these attacks. 713 8.2.4. Certification Authority 715 A Certification Authority trusted to issue certificates for the XMPP- 716 Grid Controller and/or XMPP-Grid Platforms can mount several attacks: 718 o Issue certificates for unauthorized parties, enabling them to 719 impersonate authorized parties such as the XMPP-Grid Controller or 720 an XMPP-Grid Platform. This can lead to all the threats that can 721 be mounted by the certificate's subject. 723 o Issue certificates without following all of the CA's policies. 724 Because this can result in issuing certificates that can be used 725 to impersonate authorized parties, this can lead to all the 726 threats that can be mounted by the certificate's subject. 728 o Fail to revoke previously issued certificates that need to be 729 revoked. This can lead to undetected impersonation of the 730 certificate's subject or failure to revoke authorization of the 731 subject, and therefore can lead to all of the threats that can be 732 mounted by that subject. 734 o Fail to regularly and securely distribute certificate revocation 735 information. This can cause a relying party to accept a revoked 736 certificate, leading to undetected impersonation of the 737 certificate's subject or failure to revoke authorization of the 738 subject, and therefore can lead to all of the threats that can be 739 mounted by that subject. It can also cause a relying party to 740 refuse to proceed with a transaction because timely revocation 741 information is not available, even though the transaction should 742 be permitted to proceed. 744 o Allow the CA's private key to be revealed to an unauthorized 745 party. This can lead to all the threats above. Even worse, the 746 actions taken with the private key will not be known to the CA. 748 o Fail to promptly detect and report errors and violations of trust 749 so that relying parties can be promptly notified. This can cause 750 the threats listed earlier in this section to persist longer than 751 necessary, leading to many knock-on effects. 753 8.3. Countermeasures 755 Below are countermeasures for specific attack scenarios to the XMPP- 756 Grid infrastructure. 758 8.3.1. Securing the XMPP-Grid Data Transfer Protocol 760 To address network attacks, the XMPP-Grid data transfer protocol 761 described in this document requires that the XMPP-Grid messages MUST 762 be carried over TLS (minimally TLS 1.2 [RFC5246]) as described in 763 [RFC6120] and updated by [RFC7590]. The XMPP-Grid Platform MUST 764 verify the XMPP-Grid Controller's certificate and determine whether 765 the XMPP-Grid Controller is trusted by this XMPP-Grid Platform before 766 completing the TLS handshake. The XMPP-Grid Controller MUST 767 authenticate the XMPP-Grid Platform either using the SASL EXTERNAL 768 mechanism or using the SASL SCRAM mechanism (with the SCRAM-SHA- 769 256-PLUS variant being preferred over the SCRAM-SHA-256 variant and 770 SHA-256 variants [RFC7677] being preferred over SHA-1 varients 771 [RFC5802]). XMPP-Grid Platforms and XMPP-Grid Controllers using 772 mutual certificate-based authentication SHOULD each verify the 773 revocation status of the other party's certificate. All XMPP-Grid 774 Controllers and XMPP-Grid Platforms MUST implement both SASL EXTERNAL 775 and SASL SCRAM. The selection of which XMPP-Grid Platform 776 authentication technique to use in any particular deployment is left 777 to the administrator. 779 These protocol security measures provide protection against all the 780 network attacks listed in the above document section except denial of 781 service attacks. If protection against these denial of service 782 attacks is desired, ingress filtering, rate limiting per source IP 783 address, and other denial of service mitigation measures can be 784 employed. In addition, an XMPP-Grid Controller MAY automatically 785 disable a misbehaving XMPP-Grid Platform. 787 8.3.2. Securing XMPP-Grid Platforms 789 XMPP-Grid Platforms can be deployed in locations that are susceptible 790 to physical attacks. Physical security measures can be taken to 791 avoid compromise of XMPP-Grid Platforms, but these are not always 792 practical or completely effective. An alternative measure is to 793 configure the XMPP-Grid Controller to provide read-only access for 794 such systems. The XMPP-Grid Controller SHOULD also include a full 795 authorization model so that individual XMPP-Grid Platforms can be 796 configured to have only the privileges that they need. The XMPP-Grid 797 Controller MAY provide functional templates so that the administrator 798 can configure a specific XMPP-Grid Platform as a DHCP server and 799 authorize only the operations and metadata types needed by a DHCP 800 server to be permitted for that XMPP-Grid Platform. These techniques 801 can reduce the negative impacts of a compromised XMPP-Grid Platform 802 without diminishing the utility of the overall system. 804 To handle attacks within the bounds of this authorization model, the 805 XMPP-Grid Controller MAY also include rate limits and alerts for 806 unusual XMPP-Grid Platform behavior. XMPP-Grid Controllers SHOULD 807 make it easy to revoke an XMPP-Grid Platform's authorization when 808 necessary. Another way to detect attacks from XMPP-Grid Platforms is 809 to create fake entries in the available data (honeytokens) which 810 normal XMPP-Grid Platforms will not attempt to access. The XMPP-Grid 811 Controller SHOULD include auditable logs of XMPP-Grid Platform 812 activities. 814 To avoid compromise of XMPP-Grid Platform, XMPP-Grid Platform SHOULD 815 be hardened against attack and minimized to reduce their attack 816 surface. They should be well managed to minimize vulnerabilities in 817 the underlying platform and in systems upon which the XMPP-Grid 818 Platform depends. Personnel with administrative access should be 819 carefully screened and monitored to detect problems as soon as 820 possible. 822 8.3.3. Securing XMPP-Grid Controllers 824 Because of the serious consequences of XMPP-Grid Controller 825 compromise, XMPP-Grid Controllers need to be especially well hardened 826 against attack and minimized to reduce their attack surface. They 827 need to be well managed to minimize vulnerabilities in the underlying 828 platform and in systems upon which the XMPP-Grid Controller depends. 829 Network security measures such as firewalls or intrusion detection 830 systems can be used to monitor and limit traffic to and from the 831 XMPP-Grid Controller. Personnel with administrative access ought to 832 be carefully screened and monitored to detect problems as soon as 833 possible. Administrators SHOULD NOT use password-based 834 authentication but should instead use non-reusable credentials and 835 multi-factor authentication (where available). Physical security 836 measures ought to be employed to prevent physical attacks on XMPP- 837 Grid Controllers. 839 To ease detection of XMPP-Grid Controller compromise should it occur, 840 XMPP-Grid Controller behavior should be monitored to detect unusual 841 behavior (such as a reboot, a large increase in traffic, or different 842 views of an information repository for similar XMPP-Grid Platforms). 843 XMPP-Grid Platforms should log and/or notify administrators when 844 peculiar XMPP-Grid Controller behavior is detected. To aid forensic 845 investigation, permanent read-only audit logs of security-relevant 846 information (especially administrative actions) should be maintained. 847 If XMPP-Grid Controller compromise is detected, a careful analysis 848 should be performed of the impact of this compromise. Any reusable 849 credentials that can have been compromised should be reissued. 851 8.3.4. Broker Access Models for Topics 853 The XMPP publish-subscribe specification [XEP-0060] defines five 854 access models for subscribing to Topics at a Broker: open, presence, 855 roster, authorize, and whitelist. The first model allows 856 uncontrolled access and the next two models are appropriate only in 857 instant-messaging applications. Therefore, a Broker SHOULD support 858 only the authorize model (under which the Topic owner needs to 859 approve all subscription requests and only subscribers can retrieve 860 data items) and the whitelist model (under which only preconfigured 861 Platforms can subscribe or retrieve data items). In order to ease 862 the deployment burden, subscription approvals and whitelist 863 management can be automated (e.g, the Topic "owner" can be a policy 864 server). The choice between "authorize" and "whitelist" as the 865 default access model is a matter for local service policy. 867 8.3.5. Limit on Search Result Size 869 While XMPP-Grid is designed for high scalability to 100,000s of 870 Platforms, an XMPP-Grid Controller MAY establish a limit to the 871 amount of data it is willing to return in search or subscription 872 results. This mitigates the threat of an XMPP-Grid Platform causing 873 resource exhaustion by issuing a search or subscription that leads to 874 an enormous result. 876 8.3.6. Securing the Certification Authority 878 As noted above, compromise of a Certification Authority (CA) trusted 879 to issue certificates for the XMPP-Grid Controller and/or XMPP-Grid 880 Platforms is a major security breach. Many guidelines for proper CA 881 security have been developed: the CA/Browser Forum's Baseline 882 Requirements, the AICPA/CICA Trust Service Principles, etc. The CA 883 operator and relying parties should agree on an appropriately 884 rigorous security practices to be used. 886 Even with the most rigorous security practices, a CA can be 887 compromised. If this compromise is detected quickly, relying parties 888 can remove the CA from their list of trusted CAs, and other CAs can 889 revoke any certificates issued to the CA. However, CA compromise may 890 go undetected for some time, and there's always the possibility that 891 a CA is being operated improperly or in a manner that is not in the 892 interests of the relying parties. For this reason, relying parties 893 may wish to "pin" a small number of particularly critical 894 certificates (such as the certificate for the XMPP-Grid Controller). 895 Once a certificate has been pinned, the relying party will not accept 896 another certificate in its place unless the Administrator explicitly 897 commands it to do so. This does not mean that the relying party will 898 not check the revocation status of pinned certificates. However, the 899 Administrator can still be consulted if a pinned certificate is 900 revoked, since the CA and revocation process are not completely 901 trusted. 903 8.4. Summary 905 XMPP-Grid's considerable value as a broker for security-sensitive 906 data exchange distribution also makes the protocol and the network 907 security elements that implement it a target for attack. Therefore, 908 strong security has been included as a basic design principle within 909 the XMPP-Grid design process. 911 The XMPP-Grid data transfer protocol provides strong protection 912 against a variety of different attacks. In the event that an XMPP- 913 Grid Platform or XMPP-Grid Controller is compromised, the effects of 914 this compromise have been reduced and limited with the recommended 915 role-based authorization model and other provisions, and best 916 practices for managing and protecting XMPP-Grid systems have been 917 described. Taken together, these measures should provide protection 918 commensurate with the threat to XMPP-Grid systems, thus ensuring that 919 they fulfill their promise as a network security clearing-house. 921 9. Privacy Considerations 923 XMPP-Grid Platforms can publish information about endpoint health, 924 network access, events (which can include information about what 925 services an endpoint is accessing), roles and capabilities, and the 926 identity of the end user operating the endpoint. Any of this 927 published information can be queried by other XMPP-Grid Platforms and 928 could potentially be used to correlate network activity to a 929 particular end user. 931 Dynamic and static information brokered by an XMPP-Grid Controller, 932 ostensibly for purposes of correlation by XMPP-Grid Platforms for 933 intrusion detection, could be misused by a broader set of XMPP-Grid 934 Platforms which hitherto have been performing specific roles with 935 strict well-defined separation of duties. 937 Care needs to be taken by deployers of XMPP-Grid to ensure that the 938 information published by XMPP-Grid Platforms does not violate 939 agreements with end users or local and regional laws and regulations. 940 This can be accomplished either by configuring XMPP-Grid Platforms to 941 not publish certain information or by restricting access to sensitive 942 data to trusted XMPP-Grid Platforms. That is, the easiest means to 943 ensure privacy or protect sensitive data, is to omit or not share it 944 at all. 946 Another consideration for deployers is to enable end-to-end 947 encryption to ensure the data is protected from the data layer to 948 data layer and thus protect it from the transport layer. 950 10. Operations and Management Considerations 952 In order to facilitate the management of Providers and the onboarding 953 of Consumers, it is helpful to generate the following ahead of time: 955 o Agreement between the operators of Provider services and the 956 implementers of Consumer software regarding identifiers for common 957 Topics (e.g., these could be registered with the XMPP Software 958 Foundation's registry of well-known nodes for service discovery 959 and publish-subscribe located at ). 962 o Security certificates (including appropriate certificate chains) 963 for Controllers, including identification of any Providers 964 associated with the Controllers (which might be located at 965 subdomains). 967 o Consistent and secure access control policies for publishing and 968 subscribing to Topics. 970 These matters are out of scope for this document but ought to be 971 addressed by the XMPP-Grid community. 973 11. Acknowledgements 975 The authors would like to acknowledge the contributions, authoring 976 and/or editing of the following people: Joseph Salowey, Lisa 977 Lorenzin, Clifford Kahn, Henk Birkholz, Jessica Fitzgerald-McKay, 978 Steve Hanna, and Steve Venema. In addition, we want to thank Takeshi 979 Takahashi, Panos Kampanakis, Adam Montville, Chris Inacio, and Dave 980 Cridland for reviewing and providing valuable comments. 982 12. References 984 12.1. Normative References 986 [I-D.ietf-sacm-terminology] 987 Birkholz, H., Lu, J., Strassner, J., and N. Cam-Winget, 988 "Secure Automation and Continuous Monitoring (SACM) 989 Terminology", draft-ietf-sacm-terminology-14 (work in 990 progress), December 2017. 992 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 993 Requirement Levels", BCP 14, RFC 2119, 994 DOI 10.17487/RFC2119, March 1997, 995 . 997 [RFC6120] Saint-Andre, P., "Extensible Messaging and Presence 998 Protocol (XMPP): Core", RFC 6120, DOI 10.17487/RFC6120, 999 March 2011, . 1001 [RFC7590] Saint-Andre, P. and T. Alkemade, "Use of Transport Layer 1002 Security (TLS) in the Extensible Messaging and Presence 1003 Protocol (XMPP)", RFC 7590, DOI 10.17487/RFC7590, June 1004 2015, . 1006 [RFC7677] Hansen, T., "SCRAM-SHA-256 and SCRAM-SHA-256-PLUS Simple 1007 Authentication and Security Layer (SASL) Mechanisms", 1008 RFC 7677, DOI 10.17487/RFC7677, November 2015, 1009 . 1011 [XEP-0004] 1012 Eatmon, R., Hildebrand, J., Miller, J., Muldowney, T., and 1013 P. Saint-Andre, "Data Forms", XSF XEP 0004, August 2007. 1015 [XEP-0030] 1016 Hildebrand, J., Millard, P., Eatmon, R., and P. Saint- 1017 Andre, "Service Discovery", XSF XEP 0030, July 2010. 1019 [XEP-0060] 1020 Millard, P., Saint-Andre, P., and R. Meijer, "Publish- 1021 Subscribe", XSF XEP 0060, December 2017. 1023 12.2. Informative References 1025 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security 1026 (TLS) Protocol Version 1.2", RFC 5246, 1027 DOI 10.17487/RFC5246, August 2008, 1028 . 1030 [RFC5802] Newman, C., Menon-Sen, A., Melnikov, A., and N. Williams, 1031 "Salted Challenge Response Authentication Mechanism 1032 (SCRAM) SASL and GSS-API Mechanisms", RFC 5802, 1033 DOI 10.17487/RFC5802, July 2010, 1034 . 1036 [RFC7970] Danyliw, R., "The Incident Object Description Exchange 1037 Format Version 2", RFC 7970, DOI 10.17487/RFC7970, 1038 November 2016, . 1040 [RFC8274] Kampanakis, P. and M. Suzuki, "Incident Object Description 1041 Exchange Format Usage Guidance", RFC 8274, 1042 DOI 10.17487/RFC8274, November 2017, 1043 . 1045 Authors' Addresses 1047 Nancy Cam-Winget (editor) 1048 Cisco Systems 1049 3550 Cisco Way 1050 San Jose, CA 95134 1051 USA 1053 Email: ncamwing@cisco.com 1055 Syam Appala 1056 Cisco Systems 1057 3550 Cisco Way 1058 San Jose, CA 95134 1059 USA 1061 Email: syam1@cisco.com 1062 Scott Pope 1063 Cisco Systems 1064 5400 Meadows Road 1065 Suite 300 1066 Lake Oswego, OR 97035 1067 USA 1069 Email: scottp@cisco.com 1071 Peter Saint-Andre 1072 Mozilla 1074 Email: stpeter@mozilla.com